This invention relates generally to rotary joints or connectors for passing information and/or power signals across a rotary-stationary interface, particularly such as passing optical signals through a plurality of optical fibers. More specifically, this invention relates to an improved rotary joint of the fiber optic type, wherein the rotary joint is designed to provide a relatively large finite turn capacity in a compact joint structure.
Fiber optic technology has undergone significant expansion in recent years, particularly for use in conveying communication data, voice data, and other information. In some applications, however, it is necessary to connect optical fibers across a rotary-stationary interface so that optical signals can be transmitted without interruption between rotating and stationary frames of reference.
In many rotary joint applications for fiber optic systems, infinite rotary turn capacity is not required. Instead, the rotary joint can be designed to accommodate a finite number of turns. One such rotary joint having a finite turn capacity is shown and described in U.S. Pat. No. 5,078,466, wherein an elongated fiber optic tape is coiled within a cylindrical housing with opposite ends of the tape connected respectively to a pair of fiber optic cables at a rotary inner hub and a stationary outer rim on the housing. The fiber optic tape thus provides an optical link for uninterrupted passage of optical signals between said cables. The length of the tape coiled within the housing is chosen to accommodate a selected finite number of turns as the rotary hub is driven in opposite directions. This rotary joint is useful, for example, in an application wherein a plurality of sensors are mounted along the length of a cable stored on a rotatable drum, and sensor signals are carried by optical fibers; from the sensors to a stationary monitor. The sensor cable is rotated in opposite directions through a finite number of turns to reel the sensor cable in and out, with the rotary joint providing for uninterrupted passage of optical signals across the rotary-stationary interface defined by the rotating drum and the stationary monitor.
While the fiber optic rotary joint of the U.S. Pat. No. 5,078,466 functions beneficially in certain finite turn count applications, practical considerations effectively limit the turn count capacity to a relatively small number. That is, the fiber optic tape is spirally coiled within the housing in the configuration of a watch mainspring, and the tape is designed with a length and stiffness to accommodate a desired turn count without tape buckling or excess friction as adjacent tape coils slide over one another. Attempts to increase turn count capacity have required significant and undesirable increases in tape length and stiffness, as well as increases in the diametric size of the rotary joint.
The present invention pertains to an improved fiber optic rotary joint of the general type described in U.S. Pat. No. 5,078,466, wherein the turn count capacity is significantly increased and/or the diametric size of the rotary joint structure is significantly decreased, and further wherein tape buckling and friction problems are substantially eliminated.